Objectives in this research are to evaluate a promising index of "current coping capacity" as a predictor of response to methadone maintenance treatment among narcotic addicts; to examine the potential modifying influence of client motivation on these predictions; to compare the predictive validity of the coping capacity index with that of other, traditionally-employed predictors; to assess the modifiability of coping capacity; to validate the coping capacity construct within a narcotic addict population; and to construct and cross-validate an instrument for assessing coping capacity that maximizes predictive validity and minimizes administration and scoring time. In the first phase of the study coping capacity will be assessed for 120 addicts at methadone stabilization and again six months later. Case history information, objective test measures of intelligence and psychopathology, motivation ratings and objective indices of in-treatment and follow-up adjustment will be obtained for each patient. Standard correlational methods, analysis-of-varience designs and step-wise multiple regression analyses will be employed to test hypotheses relevant to the first five objectives. A portion of these results will be used in a second phase to construct a new instrument for assessing coping capacity, which will be cross-validated on an independent but comparable sample of 45 addicts to accomplish the final objective.